The Hoan Kiem Lake, also known as Sword Lake, is considered the soul of the city. Now that soul may need purification.

The oxygen level is running low and the lake is no longer capable of restoring itself, officials said.

Sanitation workers come to collect trash every day but the pollution problem remains.

A dead fish next to bottles, boxes and plastic bags.

Trash often builds up in this storm sewer pipe which brings rainwater into the lake.

The pH level was recorded in mid-February at around 9.0, too alkaline for many species.

A study by the Vietnam Academy of Science and Technology showed that the already small population of creatures in the lake is shrinking and that the thick mud at the bottom of the lake contains heavy metals and toxins.

Hanoi Sewerage and Drainage Limited Company is working on a cleanup project, which includes dredging work and waste disposal for nearly 70 days.

The company also tries purifying the water with Redoxy-3C, a chemical that has been used for other contaminated lakes around Hanoi.